MICROBIAL MECHANISM OF EFFECTS OF WATER PERCOLATION ON Eh, IRON, AND NITROGEN TRANSFORMATION IN THE SUBMERGED PADDY SOILS

概要

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Effects of percolating of water through the submerged paddy fields were analyzed by laboratory experiments. Soil samples were taken from the surface layer of three kinds of paddy soil with varying amounts of easily decomposable organic substances. The air-dried soil samples put in glass vessels were incubated under submerged conditions. One series of the submerged soil was percolated with water (percolated plot) and another series was held under stagnant water (nonpercolated plot). Complex nature of the effects of the percolating water on the soil dynamics is fairly well clarified. If a soil contains large amount of easily decomposable organic substances, both supply of molecular oxygen and removal of water-soluble toxic substances are considered to enhance microbial activities and lead to increase in formation of ammonium and ferrous iron and decrease in Eh of the soil. Meanwhile, if a soil contains small amount of easily decomposable organic substances, supply of molecular oxygen will oxidizes the upper part of the soil column and removal of water-soluble substrates available for microorganisms may depress microbial activities leading to decrease in formation of ferrous iron and increase in Eh of the upper part of the soil, where most of the supplied oxygen is consumed.
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